Androgens and immune function in human and nonhuman primates

As proximate drivers of reproductive effort in males, androgens play a crucial component in male life history strategies. Androgens act in a pleiotropic fashion to modulate energy balance between competing demands like immunocompetence and reproductive processes, and investment in competing functions vary according to environmental and social contexts. Testosterone in particular is well known for its hypothesized immunosuppressive properties. We review several studies that present evidence such as positive associations between testosterone levels and infection severity, negative associations between testosterone levels and some measures of immunity, and altered levels of testosterone during infection. We also present conflicting data, illustrating that testosterone likely does not affect all aspects of immunity equally, and may in fact exhibit a phenotypic correlation with immunity in healthy individuals. The relationships between testosterone and immunity also likely depend on host energy flux in addition to other hormone levels. In particular, the adrenal androgen dehydroepiandrosterone has been implicated in immunological outcomes, and may in fact counteract some of the immunosuppressive properties of testosterone. Preliminary evidence also suggests that dehydroepiandrosterone may be elevated during immune activation. Given that one of the primary roles of dehydroepiandrosterone is to function as a reservoir for the synthesis of testosterone and other hormones, the relative differences in concentrations between these hormones may play an important role in immunological outcomes and life history trade-offs. A more cohesive understanding of the interactions between testosterone and dehydroepiandrosterone in varying social and ecological contexts may shed light on the larger aspects of male life history strategies.